The present invention relates to a stereo sound system that provides a good stereophonic effect for a listener who is at a position off the bisecting line of the line connecting the right and left speakers producing the stereo signals.
A stereo sound system uses two independent channels of information and produces a stereophonic effect by reproducing the respective signals from two speakers spaced apart by a predetermined distance. The conventional stereo sound system provides a good stereophonic effect for a listener who is at a position on the bisecting line of the line connecting the two speakers, but not for a listener who is at a position off that bisecting line. This presents a particularly great problem with a stereo sound system installed in an automobile where the passengers' positions with respect to the system are fixed.
An improved stereo sound system which has been proposed for solving this problem is illustrated in FIG. 1. This system is characterized by arranging five speakers, i.e. two speakers 1 and 2 for reproducing the right and left signals R and L, and three additional speakers 3, 4 and 5 positioned between these two speakers. The system also includes a divider 6 that divides the signals from the right and left channels into three portions which are supplied to the respective speakers 3, 4 and 5 from positions that correspond to those of these speakers. Because of the arrangement of the five speakers over a wide range, this improved system claims a better stereophonic effect. Furthermore, the acoustic images are evenly distributed among the five speakers and provide a good balance of sound volumes, and hence, the range where the sound is audible with a good stereophonic effect is slightly expanded.
However, unless the spacing of each speaker is increased, the volume of the sound coming from the three intermediate speakers cancel the sound from the right and left speakers to reduce the spatial distribution of the sound sources. This makes the above-described stereo sound system unsuitable for installation in a limited space such as in an automobile. An attempt has been made to produce a similar stereo sound system using three speakers, two speakers arranged on the right and left sides, and one central speaker. If the volume of the sound from the center speaker is increased in order to provide a better stereophonic effect at a position off the bisecting line of the imaginary line connecting the right and left speakers (said position is sometimes hereunder referred to as the off-line position), the acoustic image that should be oriented at the center comes slightly closer to the center, but the volume of the sound coming from the center speaker becomes so high that the sense of spatial distribution of the sound sources is reduced. Furthermore, if the listener is at the off-line position indicated by reference numeral 7 in FIG. 1, the greater part of the sound he can hear is due to the acoustic images 8 and 9 from nearby speakers, and only a weak acoustic image 10 comes from the other speaker or speakers.